1. Technical Field
The present disclosure relates to a method of manufacturing a display device, and more particularly, to a method of manufacturing an organic light emitting diode (OLED) display capable of suppressing damage to pad electrodes.
2. Description of the Related Art
An organic light emitting diode (OLED) display displays an image by driving an organic light emitting element. The organic light emitting element includes an anode (e.g., hole injection electrode), an organic emission layer, and a cathode (e.g., electron injection electrode). When electrons and holes are injected to the organic emission layer respectively by the anode and the cathode, an exciton, which is a combination of an electron and a hole, is generated in the organic emission layer. Light is emitted by energy produced when the exciton relaxes from an exited state to a ground state.
An active matrix type OLED display generally has a substrate including a pixel area and a pad area, wherein an image is displayed in the pixel area, and the pad area is formed outside the pixel area. An external module is mounted on pad electrodes formed in the pad area. In the pixel area, red, green, and blue organic light emitting elements are disposed in a matrix form. At least two thin film transistors (hereinafter, referred as “TFTs”) are provided for each organic light emitting element so that each organic light emitting element can be independently controlled.
In general, the OLED display is manufactured by using processes of: (1) forming a TFT including an active layer, a gate electrode, a source electrode, and a drain electrode on a substrate; (2) forming a planarization layer to cover the TFT; (3) forming a first pixel electrode on the planarization layer coupled to the drain electrode; and (4) forming an organic emission layer and a second pixel electrode on the first pixel electrode. The pad electrodes are formed in the pad area in the process of forming the TFT. The pad electrodes are covered with at least one insulation layer. Further, the pad electrodes are exposed on the substrate through an opening formed in the insulation layer(s).
In the aforementioned manufacturing processes, however, the first pixel electrode is formed in a state in which the pad electrodes are exposed. Therefore, the pad electrodes may be damaged by a first pixel electrode etchant. That is, if the pad electrodes comprise a material that is etched by the first pixel electrode etchant, the pad electrodes may be etched during etching of the first pixel electrode, which may cause disconnection of the pad electrodes.